β-mercaptocarboxylic acid is a compound which is useful as a raw material for organic synthesis products including agricultural chemicals, and pharmaceuticals, and is useful as a raw material for a stabilizer of vinyl chloride, a cross-linking agent of an epoxy resin and an acrylic acid ester polymer, and a plastic lens monomer.
Examples of the process for preparing β-mercaptocarboxylic acid are as follows.
Patent Document 1 discloses a method in which acrylic acid and thiosulfate are reacted in an aqueous medium, as a result to produce Bunte salt as a precursor of β-mercaptopropionic acid, and then, the Bunte salt is hydrolyzed in the presence of an acid.
Patent Document 2 discloses a method in which an acrylic acid alkali salt aqueous solution is added to an aqueous solution of alkali hydrosulfide to react in the presence of an alkali hydroxide, the resultant is neutralized with an acid, and a reduction treatment is performed thereto with zinc.
Patent Document 3 discloses a method in which, in a method in which unsaturated carboxylic acid and a hydrogen sulfide compound are reacted, the obtained reaction medium is acidified to produce mercaptocarboxylic acid, hydrogen sulfide other than hydrogen sulfide provided in the neutralization of the unsaturated carboxylic acid is supplied, and the reaction is performed under the pressurization of at least 8 bar. In addition, Patent Document 3 discloses that a hydrogen sulfide compound is obtained by the reaction of H2S and sodium hydroxide.
Patent Document 4 discloses a method in which β-unsaturated carboxylic acid and hydrogen sulfide are reacted in an aqueous solution in the presence of a basic compound to produce β-mercaptocarboxylic acid, and the above-described reaction is performed under pressure conditions of 3.5 MPaG to 20.0 MPaG.
Patent Document 5 discloses a method in which when unsaturated nitrile is added to an aqueous solution of alkali hydrosulfide to react, the resultant is neutralized, and is hydrolyzed to prepare mercaptocarboxylic acid, sulfur is used.
Patent Document 6 discloses a method in which after alkali hydroxide is added to thiodipropionic acid to make an alkali salt, the resultant is mixed with an aqueous alkali sulfide solution, and acidification is performed to prepare β-mercaptopropionic acid.